1. Field of the Invention
The present invention relates in general to a four-cycle engine having a rocker arm inserted between a valve actuating cam disposed on a camshaft and an engine valve, the rocker arm being rockably supported on a rocker shaft having an axis in parallel with the camshaft, and a rocker shaft support portion integrally formed on a cylinder head so as to be disposed between the engine valve and the camshaft as viewed from an axial direction of the camshaft and the rocker shaft, the rocker shaft support portion supporting the rocker shaft. More particularly, the present invention relates to an improved rocker shaft support structure.
2. Description of Background Art
A four-cycle engine is disclosed, for example, in Japanese Patent Laid-Open No. 2004-100651, in which an exhaust valve is driven to open or close by a rocker arm that rocks by being driven by rotation of an exhaust-side valve actuating cam disposed on a camshaft.
In such a four-cycle engine, enhancing stiffness of the rocker shaft support portion supporting the rocker shaft, on which a driving force from the side of the valve actuating cam and a reaction force from the engine valve act, is necessary for enhancing an operating response of the engine valve. To achieve that purpose, it is preferable to enhance the stiffness of the rocker shaft support portion without inviting an increase in the size of the cylinder head.